Diving Duck’s solution is brilliant, the best yet. I suffered with alignment issues ( out of plum final holes, which drilling 1/2 way through from the top would have prevented), moving the teardrop forward and backwards over the trailer, then epoxy coating those holes that I felt were too near or touching the wood. 5/8″ for the fill holes would have prevented this even with the misalignment. I did 5/8″ holes for my storage box – much better. I put silicone around the upper 3/4″ of the bolts before inserting them in the camper floor.The weight of the camper on the neoprene washers should keep the moisture out from the underside with or without silicone. I suspended my teardrop on styrofoam blocks 1/4″ above the final resting position to get the neoprene washers and risers lined up with the bolts unassisted.